This invention relates to a fastener driving device and, more particularly, to an air operated fastener driving device having interchangeable control modules.
A conventional fastener driving device typically includes a main valve disposed above a cylinder sleeve which houses a piston and cylinder unit. The main valve is pilot pressure operated and movable from a closed position to an opened position permitting air under pressure to communicate with the piston and cylinder unit for initiating a fastener drive stroke. This main valve/sleeve valve arrangement has proven to be efficient, but adds to the overall height of the device, which may be unacceptable for certain applications.
It is also known that conventional fastener driving devices may be one of several types. In accordance with a first type of driving device, conventionally referred to as one containing a "standard" valve arrangement, the piston undergoes a fastener impacting stroke upon actuation of the trigger. In this device, the piston does not return to its initial or upper position until after the trigger is released.
Although the standard device is appropriate for certain applications, the operator may actuate the trigger longer than needed to drive a fastener which causes air over the piston to increase. This pressure may reach line pressure. Thus, the high pressure over the piston must be exhausted during the return stoke of the piston which tends to be noisy. Further, air consumption is high with trigger fire tools due to having to exhaust such high pressures. In addition, since high pressure may be unnecessarily applied to the piston which contacts a bumper of the tool at the end of the drive stroke, bumper life is reduced.
With trigger fire tools, if the operator actuates the trigger longer than needed, the driving element remains exposed or extending from the nose piece of the tool. When the operator moves from one position to another, the tip of the fastener driving element may be damaged or broken. Still further, if the tool is an upholstery tool, the exposed tip of the fastener driving element may catch on the upholstery and thereby damage the fabric.
A second type of fastener driving device, know as a device having a "full cycle" valve arrangement, has been developed such that one full cycle (a single full cycle) of operation of the tool is completed while the trigger remains actuated. Thus, air over the piston remains relatively low, less than line pressure. This reduces noise and increases bumper life. Further, the fastener driving element is only exposed from the nose piece for a very short time, which eliminates the above-mentioned problems.
There also exists a third type of fastener driving devices, which operates in an automatic mode. To operate the driving device in an automatic mode of operation, a pressure responsive secondary valve is typically provided. With this arrangement, when a manually operable trigger is actuated and held, the main valve and the secondary valve operate alternately to intake air into the piston chamber and subsequently discharge the air therefrom, so that the movement of the piston and fastener driving element is repeated.
A fourth fastener driving device can be remotely operated by coupling the device in appropriate fashion to a remote actuating unit the provides alternating high and low pressure signals for generating alternating fastener drive strokes and return strokes.
A limitation with each of these fastener driving tools is that they are constructed to operate in a single mode only and cannot be easily adapted to operate in two or more modes. Since there are some instances when an operator would like to change the mode of operation, there exists a need to provide a fastener driving device which can be easily and efficiently converted between the different modes of operation.